1. Field of the Invention
The present invention relates to a servo motor with a built-in drive circuit. In particular, the present invention relates to a novel improvement of a servo motor for attaining a reduction in size and in numbers of wiring lines. The improvement can be achieved such that when, at a time power is off, a brake is engaged, positional data at that time obtained from an absolute encoder is stored in a nonvolatile memory, and multiple-rotation data is read from the nonvolatile memory when the power is turned on.
2. Description of the Related Art
A motor encoder construction may be mentioned as an example of a conventionally used servo motor with a built-in drive circuit of this type (see, for example, JP 62-278408 A and U.S. Pat. No. 5,912,541).
In the motor encoders as disclosed in JP 62-278408 A and U.S. Pat. No. 5,912,541, the motor portion is integrated with the encoder, and the drive circuit portion as the driver is constructed in a form of a casing separate from the motor main body.
The conventional servo motors, constructed as described above, have the following problems.
Regarding the built-in absolute encoder, all the angle data thereof is output to the exterior through lines; and when the power is off, requisite absolute multiple-rotation data is output to the exterior through lines by battery back-up, so that the number of lines connected to the servo motor is rather large. In the case in which multi-channel encoders are used for a single apparatus, the number of lines connected to each encoder is very large, so that the wiring thereof requires a lot of labor.
Further, to detect positional data including a multiple-rotation counting value, a back-up power source is required, and the configuration of the encoder itself constitutes an obstruction to a reduction in size.